Re: [RFC] restore user defined min_free_kbytes when disabling thp

From: Han Pingtian
Date: Wed Jan 22 2014 - 01:05:23 EST

On Tue, Jan 21, 2014 at 10:23:51AM +0000, Mel Gorman wrote:
> On Tue, Jan 21, 2014 at 05:38:59PM +0800, Han Pingtian wrote:
> > The testcase 'thp04' of LTP will enable THP, do some testing, then
> > disable it if it wasn't enabled. But this will leave a different value
> > of min_free_kbytes if it has been set by admin. So I think it's better
> > to restore the user defined value after disabling THP.
> >
> Then have LTP record what min_free_kbytes was at the same time THP was
> enabled by the test and restore both settings. It leaves a window where
> an admin can set an alternative value during the test but that would also
> invalidate the test in same cases and gets filed under "don't do that".

Because the value is changed in kernel, so it would be better to
restore it in kernel, right? :) I have a v2 patch which will restore
the value only if it isn't set again by user after THP's initialization.
This v2 patch is dependent on the patch 'mm: show message when updating
min_free_kbytes in thp' which has been added to -mm tree, can be found

please have a look. Thanks.